Combined biohydrogen and polyhydroxyalkanoates production from sheep cheese whey by a mixed microbial culture

The present study investigates the combined production of biohydrogen and polyhydroxyalkanoates (PHA) from sheep cheese whey through a 3-stage bioprocess, i.e. dark fermentation, selection of PHA storing microorganisms, and PHA accumulation. Batch dark fermentation tests (Stage I) were performed on raw cheese whey under different pH operating conditions, avoiding either the addition of inoculum or substrate pre-treatment to support the economic and technical feasibility of the proposed process. The performance of the fermentative stage was assessed in terms of biohydrogen and soluble metabolites production yields. The dark fermentation effluent was used as organic acid-rich feedstock either for selecting and harvesting PHA storing microorganisms from a mixed microbial culture without the addition of external nutrient sources (Stage II) or for the PHA accumulation by the selected biomass (Stage III). The results of the study support the possibility of achieving combined recovery yields of 5.3 L biohydrogen and 7.6 g PHA per litre of fed sheep cheese whey in the case of optimal dark fermentation pH setting (pH = 6). Such outcomes underline the untapped potential of sheep cheese whey for the recovery of high-added value bioproducts.